Continuous process for the preparation of 2-ethyl-2-(hydroxymethyl)hexanal and 2-butyl-2-ethyl-1, 3-propanediol

ABSTRACT

Disclosed is a continuous process for the manufacture of 2-ethyl-2-(hydroxymethyl)hexanal wherein 2-ethylhexanal, formaldehyde and a tertiary amine are continuously fed to a reaction zone and crude product comprising an aqueous phase and an organic phase containing 2-ethyl-2-(hydroxymethyl)hexanal and 2-ethylhexanal is continuously removed from the reaction zone Also disclosed are processes for (1) the azeotropic distillation of the organic phase of the crude product whereby unreacted 2-ethylhexanal is recovered and (2) the catalytic hydrogenation of the refined, organic phase of the crude product to produce 2-butyl-2-ethyl-1,3-propanediol.

This is a divisional application of copending application Ser. No.07/886,917 filed May 22, 1992, which is a divisional of Ser. No.07/735,575 filed Jul. 25, 1991, U.S. Pat. No. 5,146,004.

This invention pertains to an improved process for the preparation of2-ethyl-2-(hydroxymethyl)hexanal by the condensation of 2-ethylhexanaland formaldehyde in the presence of a trialkylamine catalyst. Morespecifically, this invention pertains to a continuous process for themanufacture of 2-ethyl-2-(hydroxymethyl)hexanal wherein 2-ethylhexanal,formaldehyde and a tertiary amine are continuously fed to a reactionzone, crude product comprising an aqueous phase and an organic phasecontaining 2-ethyl-2-(hydroxymethyl)hexanal and 2-ethylhexanal iscontinuously removed from the reaction zone. This invention alsoconcerns the azeotropic distillation of the organic phase of the crudeproduct whereby unreacted 2-ethylhexanal is recovered. Finally, thisinvention provides for the catalytic hydrogenation of the refined,organic phase of the crude product to produce2-butyl-2-ethyl-1,3-propanediol.

Japanese Patent Publication 73-43,085 describes the preparation of2-ethyl-2-(hydroxymethyl)hexanal (EHMH) by the reaction of2-ethylhexanal and formaldehyde in the presence of alkali metalhydroxides at a pH of 8.0 to 11.0. The EHMH is converted to2-butyl-2-ethyl-1,3-propanediol (BEPD) by the Cannizzaro reaction usinga second equivalent of formaldehyde and alkali metal hydroxide. Thisprocess generates one equivalent of sodium formate for each equivalentof BEPD. Purification of the aqueous sodium formate stream or disposalof this stream is the major disadvantage of this process. Anotherdisadvantage is the added raw material cost occasioned by the use of anextra equivalent of formaldehyde to convert the BHMH to BEPD. BritishPatent 1,320,387 discloses the preparation of2-ethyl-2-(hydroxymethyl)hexanal by heating with vigorous agitation amixture of 2-ethylhexanal, formaldehyde and triethylamine at 90°-93° C.for eight hours. A slight stoichiometric excess of formaldehyde was usedand the amount of triethylamine employed was 4.6 weight percent based onthe total weight of the materials. Despite the eight-hour reaction timeand vigorous agitation of the batch reaction mixture, the percentconversion of 2-ethylhexanal reported was approximately 81.2. Thus, theproduct obtained contained a substantial amount of unreactedformaldehyde which can detrimentally affect the performance ofcatalysts, especially nickel catalysts, used to hydrogenate EHMH toBEPD. The presence of such substantial amounts of formaldehyde also isundesirable due to the formation of formaldehyde polymers which can foulor plug processing equipment such as piping used to transport effluentsfrom distillation columns.

We have found that 2-ethyl-2-(hydroxymethyl)hexanal may be produced atimproved rates by reacting aqueous formaldehyde with a stoichiometricexcess of 2-ethylhexanal in the presence of a tertiary amine wherein thetertiary amine functions both as a catalyst and a co-solvent. Thus, oneembodiment of the present invention is a continuous process for thepreparation of 2-ethyl-(hydroxymethyl)hexanal by the condensation of2-ethylhexanal and formaldehyde in the presence of a tertiary amine bythe steps comprising:

(1) continuously feeding to a reaction zone 2-ethylhexanal, aqueousformaldehyde and a tertiary amine, wherein (i) a stoichiometric excessof 2-ethylhexanal is fed and (ii) the feed rates of tertiary amine and2-ethyl-hexanal maintain in the reaction zone a tertiaryamine:2-ethylhexanal weight ratio of at least 0.2; and

(2) continuously removing from the reaction zone a crude product mixturecomprising (i) an aqueous phase and (ii) an organic phase containing2-ethyl-2-(hydroxymethyl)hexanal and 2-ethylhexanal.

We have found that when the weight ratio of tertiaryamine:2-ethylhexanal is maintained at a value of at least 0.2, thetertiary amine functions both as a catalyst for the condensationreaction and as a co-solvent for the 2-ethylhexanal and the aqueousformaldehyde, thereby permitting more intimate contact of the reactantsand an improved reaction rate. British Patent 1,320,387 referred toabove proposes the use of alkanols and cyclic ethers as solubilizers toimprove mixing and accelerate the reaction We have found that the use ofmethanol in the process gives little improvement in reaction rateFurthermore, the use of the proposed extraneous materials presentsrecovery and recycle problems including toxicological and environmentalconsiderations. The use of alkanols or cyclic ethers also can bedetrimental to the efficient separation of the aqueous and organicphases recovered from the reaction zone.

The 2-ethylhexanal is fed to the reaction zone in a stoichiometricexcess relative to the formaldehyde fed. Generally, the 2-ethylhexanalexcess is at least 0.1 mole percent, preferably about 0.3 to 0.6 moleexcess relative to the stoichiometric amount. The aqueous formaldehydesolution used in our novel process may contain from about 20 to 80weight percent formaldehyde and a minor amount, e.g., up to 1 weightpercent, of methanol as a stabilizer. The aqueous formaldehydepreferably contains about 30 to 50 weight percent formaldehyde.

The tertiary amine catalyst/co-solvent preferably is a trialkyl aminehaving a total carbon content of up to about 12 such as trimethylamine,triethylamine, tripropylamine and the like. As stated above, thetertiary amine and 2-ethylhexanal are fed to the reaction zone at rateswhich maintain a tertiary amine:2-hexanal weight ratio of at least 0.2in the reaction zone. Although the weight ratio of tertiaryamine:2-ethylhexanal may be as high as about 0.5, we have found thatgood production rates may be achieved by maintaining the ratio in therange of about 0.3 to 0.4.

The condensation reaction may be carried out at a temperature of about90° to 140° C. and a pressure of about 1 to 10 bars absolute. Preferredreaction conditions are a temperature of about 100° to 125° C. and apressure of about 1 to 3 bars absolute.

The practice of the condensation process provided by the presentinvention permits the preparation of EHMH at improved production rateseven though the degree of agitation which may be achieved in continuousoperation typically is substantially less than the agitation which ispossible when operating a batch process. The formation of by-productssuch as 2-ethylhexanol, formate salts, and high molecular weight estersresulting from the Tischenko reaction of EHMH is minimized. Normally,the production rate (the space-time yield) is at least 100 grams EHMHper liter hour wherein liter refers to the total volume (in liters) ofthe mixture in the reaction zone. At space-time yields of 100 g/L-hour,the process typically gives a formaldehyde conversion of at least 90mole percent which results in the organic phase of the crude reactionproduct having a formaldehyde content of less than 1.7 weight percentbased on the weight of the organic phase. It is preferred to operate theprocess in a manner to achieve space time yields of EHMH in the range ofabout 100 to 500 g/L hour while obtaining a formaldehyde conversion ofgreater than about 90 to 95 mole percent and a formaldehydeconcentration of less than 1.7 weight percent in the organic phase ofthe crude product.

The continuous condensation process may be carried out by continuouslyfeeding 2-ethylhexanal, aqueous formaldehyde and a tertiary amine,including recycle 2-ethylhexanal and tertiary amine, to a reaction zoneand continuously removing a crude product stream comprising an aqueousphase and an organic phase. The reaction zone may comprise one or morereactors designed to provide agitation of the reaction mixture, e.g.,reactors equipped with agitators, a tube reactor containing packingmaterial, recirculating reactors and the like. To obtain formaldehydeconversions of at least 90 mole percent, the residence time in thereaction zone typically is about 3.5 to 6 hours. The effluent from thereaction zone is fed to a decanter wherein all, or a substantial portionof, the aqueous phase is separated from the organic phase which containsEHMH product, tertiary amine, unreacted 2-ethylhexanal, BEPD and minoramounts of formaldehyde, the ammonium formate salt of the tertiaryamine, methanol and higher molecular weight organics such asformaldehyde condensation products and C-17 and C-18 esters[2-ethylhexanoate and 2-ethyl-2-(hydroxymethyl)hexanoate esters of2-butyl-2-ethyl-1,3-propanediol]. The aqueous phase contains theammonium formate salt of the tertiary amine which may be recovered bytreating the aqueous phase with an alkali metal hydroxide. For example,the aqueous phase may be contacted with sodium hydroxide to producesodium formate and the tertiary amine which is recovered from theresulting mixture by distillation.

In a second embodiment of the present invention, the crude organic phaseobtained in accordance with the condensation process describedhereinabove is fed continuously to an extractive, azeotropicdistillation zone to recover the tertiary amine and unreacted2-ethylhexanal. This embodiment of our invention provides a continuousprocess for the recovery of 2-ethylhexanal and tertiary amine from amixture comprising 2-ethyl-2-(hydroxymethyl)hexanal, 2-ethylhexanal,tertiary amine and water by the steps of:

(1) continuously feeding the mixture to the mid section of adistillation column;

(2) continuously feeding water to the middle or upper section of thedistillation column;

(3) continuously removing from the distillation column a vapor streamcomprising 2-ethylhexanal, tertiary amine and water;

(4) condensing the vapor stream of step (3) to obtain a two phase liquidand separating the organic phase rich in 2-ethylhexanal and tertiaryamine; and

(5) continuously removing from the lower section of the distillationcolumn a two phase mixture depleted in 2-ethylhexanal and tertiaryamine.

The extractive, azeotropic distillation zone comprises a distillationcolumn and decanters for separation of the aqueous and organic effluentsof the distillation column. The crude organic phase obtained from thecondensation process is fed continuously to the midsection of thedistillation column. Water also is fed to the distillation at or nearthe top and/or to the mid-section of the column. The distillation columnis operated at approximately atmospheric pressure, a base temperature ofabout 100° to 110° C. and a head temperature of about 96° to 98° C. tominimize decomposition of the EHMH and formation of esters via theTischenko reaction Maintaining the column head temperature at about 96°to 98° C. maximizes the amount of 2-ethylhexanal removed as vapor fromthe distillation column.

A vapor stream comprising tertiary amine and a constant boiling mixture(binary azeotrope) consisting of 48.4 weight percent 2-ethylhexanal and51.6 weight percent water and having a boiling point of 96.4° C. isremoved continuously at or near the top of the column The vapor streamis condensed and the organic phase comprising 2-ethylhexanal andtertiary amine is separated, e.g., by means of a decanter, from theresulting two-phase liquid and recycled to the condensation reactionzone. The aqueous phase of the two-phase liquid may be recycled to theupper portion of the distillation column.

A liquid stream comprised of all, or essentially all, of the EHMH fed tothe distillation column, water, BEPD and minor amounts of formaldehyde,2-ethylhexanal, and C- 17 and C- 18 esters is removed continuously fromthe base of the distillation column and fed to a decanter wherein theaqueous and organic phases of the column underflow are separated. Theaqueous phase of the underflow stream containing minor amounts of theformate salt of the tertiary amine and EHMH may be treated with analkali metal hydroxide to recover the tertiary amine for recycle to thecondensation reaction zone. The organic phases comprises a major amountof EHMH and minor amounts of water, formaldehyde, 2-ethylhexanal, andC-17 and C- 18 esters. The refined organic phase obtained from theextractive, azeotropic distillation zone preferably is comprised of atleast 80 weight percent EHMH and less than about 2 weight percentformaldehyde.

In another embodiment of the present invention, the refined organicphase is fed continuously to a hydrogenation zone wherein the EHMHcomponent of the refined organic phase is catalytically hydrogenated atelevated temperatures and pressures, according to known means, toproduce BEPD. For example, the catalysts and/or processes described inU.S. Pat. Nos. 4,097,540, 4,181,810, 4,250,337, 4,386,219, 4,393,251,4,851,592 and 4,855,515 may be used to convert the EHMH to BEPD. Thisembodiment involves a process for the preparation of BEPD by thecondensation and recovery processes described hereinabove in combinationthe hydrogenation of the EHMH to BEPD. Thus, our invention includes aprocess for the continuous preparation of2-butyl-2-ethyl-1,3-propanediol which comprises the steps of:

(1) continuously feeding to a reaction zone 2-ethylhexanal, aqueousformaldehyde and a tertiary amine, wherein (i) a stoichiometric excessof 2-ethylhexanal is fed and (ii) the feed rates of tertiary amine and2-ethylhexanal maintain in the reaction zone a tertiaryamine:2-ethylhexanal weight ratio of at least 0.2;

(2) continuously removing from the reaction zone a crude product mixturecomprising (i) an aqueous phase and (ii) an organic phase containing2-ethyl-2-(hydroxymethyl)hexanal, 2-ethylhexanal and tertiary amine;

(3) continuously feeding the organic phase of step (2) to the midsection of a distillation column;

(4) continuously feeding water to the middle or upper section of thedistillation column;

(5) continuously removing from the distillation column a vapor streamcomprising 2-ethylhexanal, tertiary amine and water;

(6) condensing the vapor stream of step (5) to obtain a two-phaseliquid, separating the organic phase rich in 2-ethylhexanal and tertiaryamine, and recycling the organic phase to the reaction zone;

(7) continuously removing from the lower section of the distillationcolumn a two-phase mixture depleted in 2-ethylhexanal and tertiaryamine;

(8) continuously separating the two-phase mixture of step (5) into (i)an aqueous phase and (ii) an organic phase rich in2-ethyl-2-(hydroxymethyl) hexanal; and

(9) continuously feeding the organic phase of step (8) to ahydrogenation zone wherein the 2-ethyl-2-(hydroxymethyl)hexanal ishydrogenated to 2-butyl-2-ethyl-1,3-propanediol in the presence of ahydrogenation catalyst.

The hydrogenation zone comprises a pressure vessel containing one ormore fixed beds of a suitable hydrogenation catalyst. The product of thehydrogenation zone may be recycled to dissipate the heat ofhydrogenation.

The hydrogenation preferably is carried out by passing the refinedorganic phase over one or more fixed beds of a supported nickel catalystat a total pressure of about 21 to 36 bars absolute and at ahydrogenation zone exit temperature of about 150° to 170° C. Thecatalyst may comprise nickel deposited on a catalyst support materialsuch as silica, alumina, carbon, titanium dioxide, molecular sieves,zeolites, kieselguhr, etc. Normally, the supported nickel catalysts arecomprised of about 1 to 90 weight percent nickel, calculated as [Ni],based on the total weight of the catalyst. Preferred nickel catalystscomprise about 1 to 70 weight percent nickel on silica/alumina.

The conversion of EHMH to BEPD in the hydrogenation zone typically isgreater than 99%, e.g., 99.7% or greater. The product of thehydrogenation zone normally comprises at least 75 weight percent BEPDand minor amounts of water, methanol, 2-ethylhexanol, BEPD2-ethylhexanoate and BEPD 2-ethyl-2-(hydroxymethyl)hexanoate. We havefound that the activity of the nickel hydrogenation catalyst does notdecline measurably over 60 days of continuous operation.

The hydrogenation product may be refined according to known purificationtechniques to obtain BEPD having a purity of 99.5% or greater. Thus, theeffluent from the hydrogenation vessel may be fed to a flash pot whereinthe pressure is reduced and essentially all of the material, except forany high boiling components present, is flashed to the mid section of afirst distillation column operated at about 200° C. under reducedpressure. Low boiling components comprising water and 2-ethylhexanol areremoved from the top of the column and remainder is removed from thebase of the column and fed to the mid section of a second distillationcolumn, also operated at 200° C. and at reduced pressure. The esterimpurities are underflowed from the second column and purified BEPD,typically containing less than 50 ppm nitrogen, is removed from the topof the column.

The accompanying Figure is a process flow diagram illustrating a systemembodying the principles of the processes of the present invention. Itis, of course, possible that the processes may be operated by modifyingthe specific processes illustrated by the Figure.

Referring to the Figure, fresh 2-ethylhexanal, aqueous formaldehyde andtertiary amine are fed continuously by means of conduits 2, 4, 6, 8, and10 to condensation reaction zone 12 along with reaction mixture recycle,fed via conduits 14, 8 and 10, and recycle 2-ethylhexanal and tertiaryamine, fed via conduits 16 and 10. The 2-ethylhexanal:formaldehyde moleratio fed by conduit 10 normally is in the range of about 1.1:1 to about1.6:1. The residence time of the reaction mixture within zone 12 isabout 3.5 to 6 hours. Crude product comprising (i) an aqueous phase and(ii) an organic phase containing 2-ethyl-2-(hydroxymethyl)hexanal and2-ethylhexanal is removed continuously from reaction zone 12 andtransported by conduit 18 to decanter 20.

The crude organic phase comprising EHMH, 2-ethylhexanal and tertiaryamine is transported by conduits 22 and 23 from decanter 20 to the midsection of extractive, azeotropic distillation column 24. Fresh water issupplied to column 24 by conduits 26 and 23 as a mixture with the crudeorganic phase and/or by conduit 28. Alternatively, a portion or all ofthe fresh water may be provided to column 24 by means of conduit 28. Thebase of column 24 is maintained at about 100° to 110° C. byrecirculating a liquid phase from the base of column 24 through lines 30and 32, reboiler 34 and line 36. Vapor comprising water, 2-ethylhexanaland tertiary amine is removed continuously from column 24 via conduit38, condensed in condenser 40 and fed by conduit 42 to decanter 44. Thetemperature of the vapor phase exiting column 24 normally is in therange of about 96° to 98° C. The organic phase comprising 2-ethylhexanaland tertiary amine is recycled via conduits 16 and 10 to reaction zone12. The aqueous phase is returned to the upper portion of distillationcolumn 24 by conduit 46.

A liquid phase comprising all, or essentially all, of the EHMH fed todistillation column 24, water and minor amounts of formaldehyde,2-ethylhexanal, and 2-ethylhexanoate and2-ethyl-2-(hydroxymethyl)hexanoate esters of2-butyl-2-ethyl-1,3-propanediol is removed continuously from the base ofcolumn 24 by conduit 30 and fed via conduit 48 to decanter 50. Therefined organic phase separated in decanter 50 is fed via conduit 52 tohydrogenation zone 54 wherein the EHMH is catalytically hydrogenated toBEPD as described hereinabove. The hydrogenation zone may comprise oneor more pressure vessels containing a supported hydrogenation catalyst.The hydrogenation preferably is carried out at a temperature of about150° to 170° C. and a pressure of about 28 to 36 bars absolute in thepresence of a supported nickel catalyst, e.g., about 50 weight percentnickel on alumina.

An important feature of the present invention is the provision of theEHMH containing, refined organic phase which contains less than (i) 2.0weight percent formaldehyde and (ii) 1.0 weight percent 2-ethylhexanal.The upper limits of formaldehyde and 2-ethylhexanal preferably are 3.0and 5.0 weight percent, respectively. The low formaldehyde concentrationpermits the use of nickel catalysts and relatively low hydrogenationpressures in hydrogenation zone 54. Nickel hydrogenation catalystsnormally are rapidly deactivated by the presence of significant amountsof formaldehyde, e.g., formaldehyde concentrations of about 3.0 weightpercent or higher, in hydrogenation feed mixtures. The lowconcentrations of 2-ethylhexanal results in the production of BEPD athigh yields e.g., 85% or greater, based on the 2-ethylhexanal fed toreaction zone 12.

Hydrogenation product is removed continuously from hydrogenation zone 54through conduit 56 and transported to a BEPD refining zone (not shown)comprising a distillation train wherein high and low boilers areseparated from the BEPD according to conventional purificationtechniques. The refined BEPD thus obtained typically has a purity of99.5% or greater and a nitrogen content of less than 50 ppm.

The aqueous phases, containing the formate salt of the tertiary amine,collected in decanters 20 and 54 are combined by means of conduits 58,60 and 62 and fed via conduit 63 to amine recovery zone 64. The tertiaryamine is liberated from the formate salt of the amine by treating theaqueous phases with an alkali metal hydroxide, supplied via line 66, andthe tertiary amine thus recovered is returned to reaction zone 12 byconduits 68, 8 and 10. An aqueous waste stream containing alkali metalformate is removed from amine recovery zone 64 for disposal in aconventional waste water treatment plant.

The processes provided by the present invention are further illustratedby the following examples.

EXAMPLES 1-3 AND COMPARATIVE EXAMPLES 1 AND 2

A one liter Parr autoclave was charged with 2-ethylhexanal (334 g, 406mL, 2.6 mole), 44% aqueous formaldehyde (136.4 g, 122 mL, 2.0 mole) andvarying amounts of triethylamine to determine the effect of increasingtriethylamine concentration on reaction rate. After purging withnitrogen, the autoclave was sealed and heated at 100° C. for one hour.The autoclave was cooled and the contents were analyzed for formaldehyde(HCHO) by calorimetric analysis and for 2-ethyl-2-(hydroxymethyl)hexanal(EHMH) by gas chromatography analysis. The yield of EHMH was calculatedbased on the 2-ethylhexanal consumed which was determined aftercorrecting the gas chromatograph area for methanol and excess2-ethylhexanal. Table I sets forth the amount of triethylamine (TEA,g/mL), the concentration by weight of triethylamine based on the totalweight of the materials charged (TEA, %), the mole percent offormaldehyde converted (HCHO Conv.) and the percent yield of EHMHobtained.

                  TABLE I                                                         ______________________________________                                                  TEA                HCHO  Yield                                      Example   g/mL      %        Conv. EHMH                                       ______________________________________                                        1         47.0/65.4 10       86    68.2                                       2         70.6/98.0 15       92    83.4                                       3          94.0/130.6                                                                             20       95    88.0                                       C-1        9.4/13.0  2       40    35.2                                       C-2       23.6/32.6  5       74    48.9                                       ______________________________________                                    

The data presented in Table I establish the beneficial effects obtainedby the use of larger amount of triethylamine. The weight ratios of thetriethylamine to 2-ethylhexanal initially fed in these batch experimentsvary from the ratios resulting from continuous operation wherein thetriethylamine and reactants are continuously consumed.

EXAMPLES 4-6 AND COMPARATIVE EXAMPLES 3 AND 4

To determine the effect of carrying out the condensation reaction in thepresence of methanol as a co-solvent, Examples 1-3 and ComparativeExamples 1 and 2 were repeated except that the reactions were carriedout in the presence of 30 weight percent methanol based on the totalweight of materials charged to the autoclave. The amounts of methanolused (MeOH, g) in each example and the triethylamine concentration, theformaldehyde conversion and yield of EHMH, as described in the precedingexamples, are set forth in Table II.

                  TABLE II                                                        ______________________________________                                                   TEA                HCHO  Yield                                     Example    %      MeOH        Conv. EHMH                                      ______________________________________                                        4          10     156         81.0  81.3                                      5          15     162         84.0  87.0                                      6          20     170         90.0  85.0                                      C-3         2     144         72.8  65.0                                      C-4         5     148         78.8  72.8                                      ______________________________________                                    

The results reported in Table II establish that the presence of methanolimproves formaldehyde conversion and yield of2-ethyl-2-(hydroxymethyl)hexanal when used in combination with lowconcentrations of triethylamine. However, superior results are achievedonly when triethylamine is used in initial concentrations of 10 to 20weight percent.

EXAMPLE 7

This example illustrates the continuous operation of the processes ofour invention employing the production system depicted in the Figure.All parts given are by weight unless stated otherwise.

Fresh 2-ethylhexanal, 44% aqueous formaldehyde and triethylamine are fedat 406.0, 271.0 and 1.66 parts per hour, respectively, to reaction zone12 via conduits 2, 4, 6, 8 and 10 along with 257.0 parts per hour2-ethylhexanal, 1.4 parts per hour formaldehyde and 132.9 parts per hourtriethylamine supplied by recycle conduits 16 and 68. Reaction zone 12comprises a plurality of recirculating reactors maintained at about 110°C. and about 4.5 bars absolute. The residence time of the reactionmixture in the reaction zone is about 3.7 hours. Crude condensationreaction mixture comprising EHMH is removed continuously from reactionzone 12 at a rate of 1085.0 parts per hour and fed to decanter 20wherein the crude organic phase is separated from the aqueous phase. Thespace time yield of EHMH averages 117 g/liter hour.

Crude organic phase is removed from decanter 20 at a rate of 920.3 partsper hour and fed to distillation column 24 via lines 22 and 23 alongwith water which is added at 150.0 parts per hour through conduit 26. Nowater is fed through conduit 28. The base of column 24 is maintained atabout 105° C., as described hereinabove, to produce an overhead vaporstream which is removed continuously via conduit 38, condensed incondenser 40 and fed by conduit 42 to decanter 44. The organic phasefrom decanter 44 comprising 2-ethylhexanal and tertiary amine isrecycled via conduits 16 and 10 to reaction zone 12 at the rate of 364.0parts per hour. The aqueous phase from decanter 44 is returned to theupper portion of column 24 by conduit 46.

A liquid phase stream is removed continuously from column 24 andtransported by conduits 30 and 48 to decanter 50 at a rate of 692.5parts per hour. The refined organic phase separated in decanter 50 isfed via conduit 52 at 541.7 parts per hour to hydrogenation zone 54wherein the EHMH is catalytically hydrogenated to BEPD using a 50%nickel on alumina catalyst. The hydrogenation is carried out in theliquid phase at a pressure of 35.5 bars absolute and a catalyst bed exittemperature of 160° C. using a trickle bed reactor. Hydrogenation zone54 included means for recycling effluent from the hydrogenation reactorto the reactor feed at a volume ratio of 10 parts effluent per partfresh feed.

The hydrogenation product of conduit 56 is flash distilled at 50 torr toremove most of the high boiling impurities. The top takeoff of the flashcolumn is fed to a second column which removes all low boilingimpurities. This column is operated at 6.5 bars absolute with a basetemperature of 200° C. The base overflow from this column is fed to therefining column This column is operated at 20 torr with a basetemperature of 210° C. BEPD of 99.7 percent purity is removed from thetop of the column and a small amount of high boiling esters is removedfrom the base of the column.

The yield of BEPD is 85 percent based on the 2-ethylhexanal, and 68percent based on the formaldehyde, fed to the reaction zone 12.Utilization of the triethylamine catalyst is very efficient with anaverage usage of 1 part by weight triethylamine per 200 parts by weightBEPD.

The compositions, by weight percent, of the mixtures present in conduits10, 16, 18, 22, 23, 42, 48, 52 and 56 during the operation of theprocesses described in Example 4 are set forth in Table III wherein HCHOis formaldehyde, HEH is 2-ethylhexanal, TEA is triethylamine, EHMH is2-ethyl-2-(hydroxymethyl) hexanal, Esters are 2-ethylhexanoate and2-ethyl-2-(hydroxymethyl)hexanoate esters of 2 butyl2-ethyl-1,3-propanediol and BEPD is 2-butyl-2-ethyl-1,3-propanediol.These mixtures also contain varying amounts of additional componentssuch as methanol, ethanol, TEA formate and formaldehyde condensationproducts, depending on the particular mixture.

                                      TABLE III                                   __________________________________________________________________________    Conduit                                                                            Water                                                                             HCHO                                                                              HEH TEA EHMH Esters                                                                            BEPD                                                                              Other                                       __________________________________________________________________________    10   14.0                                                                              2.2 34.5                                                                              12.4                                                                              28.5 1.9 3.4 3.1                                         16   1.9 0.4 70.3                                                                              24.0                                                                               1.9 --  --  1.5                                         18   13.7                                                                              0.8 23.7                                                                              8.1 33.2 2.9 6.7 10.9                                        22   2.7 0.9 27.9                                                                              9.5 39.1 3.4 7.9 8.6                                         23   16.4                                                                              0.7 24.0                                                                              8.2 33.6 2.9 6.8 7.4                                         42   49.5                                                                              0.1 22.4                                                                              10.7                                                                               0.7 --  --  16.6                                        48   22.9                                                                              0.9  1.2                                                                              0.2 50.8 5.6 10.6                                                                              7.8                                         52   8.2 1.1  1.5                                                                              0.3 65.0 7.2 13.5                                                                              3.2                                         56   8.1 --  Trace                                                                             Trace                                                                             --   7.1 78.6                                                                              6.2                                         __________________________________________________________________________

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modification can be effected within the spirit and scope of theinvention.

We claim:
 1. A continuous process for the preparation of2-butyl-2-ethyl-1,3-propanediol which comprises the steps of:(1)continuously feeding to a reaction zone 2-ethylhexanal, aqueousformaldehyde and a tertiary amine, wherein (i) a stoichiometric excessof 2-ethylhexanal is fed and (ii) the feed rates of tertiary amine and2-ethylhexanal maintain in the reaction zone a tertiaryamine:2-ethylhexanal weight ratio of at least 0.2; (2) continuouslyremoving from the reaction zone a crude product mixture comprising (i)an aqueous phase and (ii) an organic phase containing2-ethyl-2-(hydroxymethyl)hexanal, 2-ethylhexanal and tertiary amine; (3)continuously feeding the organic phase of step (2) to the mid-section ofa distillation column; (4) continuously feeding water to the middle orupper section of the distillation column; (5) continuously removing fromthe distillation column a vapor stream comprising 2-ethylhexanal,tertiary amine and water; (6) condensing the vapor stream of step (5) toobtain a two-phase liquid, separating the organic phase rich in2-ethylhexanal and tertiary amine, and recycling the organic phase tothe reaction zone; (7) continuously removing from the lower section ofthe distillation column a two-phase mixture depleted in 2-ethylhexanaland tertiary amine; (8) continuously separating the two-phase mixture ofstep (5) into (i) an aqueous phase and (ii) an organic phase rich in2-ethyl-2-(hydroxymethyl)hexanal; and (9) continuously feeding theorganic phase of step (8) to a hydrogenation zone wherein the2-ethyl-2-(hydroxymethyl)hexanal is contacted with a supported nickelhydrogenation catalyst at a total pressure of about 21 to 36 barsabsolute and at a hydrogenation zone exit temperature of about 150° to170° C. to produce 2-butyl-2-ethyl-1,3-propanediol.
 2. Process accordingto claim 1 wherein the tertiary amine is a trialkylamine containing upto about 12 carbon atoms and the reaction zone is maintained at atemperature of about 100° to 125° C. and a pressure of about 1 to 3 barsabsolute.
 3. A continuous process for the preparation of2-butyl-2-ethyl-1,3-propanediol which comprises the steps of:(1)continuously feeding to a reaction zone 2-ethylhexanal, aqueousformaldehyde and a tertiary amine, wherein (i) the mole ratio of2-ethylhexanal to formaldehyde fed to the reaction zone is about 1.1:1to 1.6:1 and (ii) the feed rates of tertiary amine and 2-ethylhexanalmaintain in the reaction zone a tertiary amine:2-ethylhexanal weightratio of about 0.2 to 0.5; (2) continuously removing from the reactionzone a crude product mixture comprising (i) an aqueous phase and (ii) anorganic phase containing 2-ethyl-2-(hydroxymethyl)hexanal and2-ethylhexanal;whereby the formaldehyde concentration of organic phase(2) (ii) is less than about 1.7 weight percent an the space-time yieldof 2-ethyl-2-(hydroxymethyl)hexanal is at least 100 g per liter-hour;(3) continuously feeding the organic phase of step (2) to themid-section of a distillation column; (4) continuously feeding water tothe middle or upper section of the distillation column; (5) continuouslyremoving from the distillation column a vapor stream comprising2-ethylhexanal, tertiary amine and water; (6) condensing the vaporstream of step (5) to obtain a two-phase liquid, separating the organicphase rich in 2-ethylhexanal and tertiary amine, and recycling theorganic phase to the reaction zone; (7) continuously removing from thelower section of the distillation column a two-phase mixture depleted in2-ethylhexanal and tertiary amine; (8) continuously separating thetwo-phase mixture of step (5) into (i) an aqueous phase and (ii) anorganic phase rich in 2-ethyl-2-(hydroxymethyl)hexanal; and (9)continuously feeding the organic phase of step (8) to a hydrogenationzone wherein the 2-ethyl-2-(hydroxymethyl)hexanal is contacted with asupported nickel hydrogenation catalyst at a total pressure of about 21to 36 bars absolute and at a hydrogenation zone exit temperature ofabout 150° to 170° C. to produce 2-butyl-2-ethyl-1,3-propanediol. 4.Process according to claim 3 wherein the base of the distillation columnis maintained at a temperature of about 100° to 110° C. and the tertiaryamine is a trialkylamine having up to about 12 carbon atoms.
 5. Acontinuous process for the preparation of2-butyl-2-ethyl-1,3-propanediol which comprises the steps of:(1)continuously feeding to a reaction zone 2-ethylhexanal, aqueousformaldehyde and a tertiary amine selected from triethylamine andtripropylamine, wherein (i) the mole ratio of 2-ethylhexanal toformaldehyde fed to the reaction zone is about 1.1:1 to 1.6:1 and (ii)the feed rates of tertiary amine and 2-ethylhexanal maintain int hereaction zone a tertiary amine:2-ethylhexanal weight ratio of about 0.2to 0.5; (2) continuously removing from the reaction zone a crude productmixture comprising (i) an aqueous phase and (ii) an organic phasecontaining 2-ethyl-2-(hydroxymethyl)hexanal and 2-ethylhexanal;wherebythe formaldehyde concentration of organic phase (2) (ii) is less thanabout 1.7 weight percent an the space-time yield of2-ethyl-2-(hydroxymethyl)hexanal is at least 100 g per liter-hour; (3)continuously feeding the organic phase of step (2) to the mid-section ofa distillation column wherein the base of the distillation column ismaintained at a temperature of about 100° to 110° C.; (4) continuouslyfeeding water to the middle or upper section of the distillation column;(5) continuously removing from the distillation column a vapor streamcomprising 2-ethylhexanal, tertiary amine and water; (6) condensing thevapor stream of step (5) to obtain a two-phase liquid, separating theorganic phase rich in 2-ethylhexanal and tertiary amine, and recyclingthe organic phase to the reaction zone; (7) continuously removing fromthe lower section of the distillation column a two-phase mixturedepleted in 2-ethylhexanal and tertiary amine; (8) continuouslyseparating the two-phase mixture of step (5) into (i) an aqueous phaseand (ii) an organic phase rich in 2-ethyl-2-(hydroxymethyl)hexanal; and(9) continuously feeding the organic phase of step (8) to ahydrogenation zone wherein the 2-ethyl-2-(hydroxymethyl)hexanal iscontacted with a supported nickel hydrogenation.
 6. Process according toclaim 5 wherein the supported nickel hydrogenation catalyst comprisesabout 1 to 70 weight percent nickel on silica/alumina.